Elodea is a genus of 6 species of aquatic plants often called the waterweeds described as a genus in 1803. Elodea is native to the Americas and is also widely used as aquarium vegetation. It lives in fresh water. The introduction of some species of Elodea into waterways in parts of Europe, Australia, Africa, Asia, and New Zealand has created a significant problem and it is now considered a noxious weed in these areas. An older name for this genus is Anacharis, which serves as a common name in North America. Elodea canadensis, sometimes called American or Canadian water weed or pond weed, is widely known as the generic water weed. The use of these names causes it to be confused with similar-looking plants, like Brazilian elodea (Egeria densa) or hydrilla (Hydrilla verticillata). American water weed is an attractive aquarium plant and is a good substitute for Brazilian elodea. It can be used for science experiments in classrooms demonstrating how plants use carbon dioxide with the usage of bromothymol blue.